An immobilized enzyme has conventionally been used in a fixed bed reactor for carrying out, by passing a liquid therethrough, a variety of reactions in relation to the production of L-aspartic acid, production of oils and fats through transesterification, hydrolysis of lactose, hydrolysis of oils and fats, or similar reactions.
These reactions relatively release low heat. Therefore, the reactions are typically carried out in a drum-type reactor, which is the simplest reactor.
As in the case of the hydrolysis of oils and fats, when liquids of two or more species are simultaneously passed through a reactor to which an enzyme has been immobilized, in order to improve reaction efficiency, the liquids are preferably mixed to a uniform state prior to the application thereof to the reactor. In this case, since an oil-phase substrate and a water-phase substrate, which are employed in hydrolysis, are essentially immiscible even after undergoing a mixing operation, in order to attain a uniform phase, they are usually prepared into an emulsion. Meanwhile, since emulsion particles are difficult to reach enzyme molecules that are adsorbed onto the pore walls of a carrier, according to some techniques, the liquid passage rate is controlled to fall within a range such that the reaction mixture will not be emulsified (see Patent Document 1).
In order to pass an oil-phase substrate and a water-phase substrate over the surfaces of a fixed bed, there have been recognized two methods; i.e., a counter flow method (see Patent Documents 1 and 2) and a parallel flow method (see Patent Document 3). Because the former method requires a special scheme and operation method, the parallel flow method is usually employed.    [Patent Document 1] JP-A-S61-85195    [Patent Document 2] JP-A-H01-98494    [Patent Document 3] JP-A-2000-160188
The present invention provides a method for producing a useful substance by supplying, to a fixed-bed reactor packed with an immobilized enzyme, a liquid mixture containing two liquid phases, in which the two liquid phases are allowed to flow in an identical, parallel direction, which method employs a fixed-bed reactor equipped with an insertion unit or tubes, so as to form a plurality of lumens in the fixed-bed reactor, each lumen having a cross section of a circular shape with a diameter of 100 mm or less or having a polygonal shape with a diagonal line of 100 mm or less, wherein the lumens are packed with an immobilized enzyme and the liquid mixture is supplied therethrough.